Current Source Converter-Based Series-Connected Offshore Wind System: Configuration, Modulation, and Control

Transcription

1 Current Source ConverterBased SeriesConnected Offshore Wind System: Configuration, Modulation, and Control Qiang Wei Laboratory for Electric Drive Applications and Research (LEDAR) Ryerson University, Canada May 10, 2018

2 Background Why offshore wind power? Considerable wind resources Higher and steadier wind speeds Smaller environmental impact 2

3 Background #1 #n Why seriesconnected configuration? 0.69/3 kv MVAC (33 kv) Offshore Substation HVDC (300 kv or more) Onshore Substation Parallelconnected configuration Offshore substation by ABB [1] 900 MW 23,000 tons 100 meters long 70 meters wide 100 meters tall #1 Lowfrequency transformer HVDC V dc #n Seriesconnected configuration 3 Onshore Substation Without offshore substation

4 Background Why current source converter? Lowfrequency transformer HVDC #1 V dc Challenge in dclink control #n Onshore Substation Voltage source converter configuration Lowfrequency transformer HVDC #1 Easy in dclink control #n Onshore Substation Current source converter configuration 4

5 CSCBased Offshore Wind Farm Objectives? Smaller size and weight Higher reliability Higher efficiency Higher dynamic performance Lower cost What I did? New configurations New modulation New control strategies 5

6 CSCBased Configuration PWM CSCBased SeriesConnected Configuration [2] MV PMSG #1 #n LowFrequency Transformer CSR L dc CSI No offshore substation Easy dclink control CSC related advantages Bulky lowfrequency transformer PWM CSR PWM CSI 6

7 CSCBased Configuration Mediumfrequency transformerbased Configuration 4000 V MV PMSG S 11 S 12 S 13 S 14 i p V dc_n L dc S 1 S 3 S 5 i w i g Transformer 690 V LV PMSG S 4 S 6 S 2 Mediumvoltage configuration [3] S 11 S 12 i p S 13 S 14 V dc_n L dc S 1 S 3 S 5 i w i g C f Transformer No offshore substation Easy dclink control CSC related advantages No lowfrequency transformer Relatively high torque ripple S 4 S 6 S 2 C f Lowvoltage configuration [4] 7

8 Modulation for CSC Modulation Requirements S 1 S 3 S 5 i w L g Thermal requirement f s = 500 Hz codes compliance f LC = pu S 4 S 6 S 2 C f Superior loworder (5 th and 7 th ) harmonics performance High dynamic performance 8

9 Modulation for CSC Modulation: SHE, TPWM, and SVM Iwn/Iw1,max% Iwn/Iw1,max% Iwn/Iw1,max% SHE@360 Hz TPWM@420 Hz SVM@540 Hz Modulation scheme Loworder harmonics Dynamic performance SHE Better Poor TPWM Good Poor SVM Poor Better Only SHE used in practice

10 Modulation for CSC Natural sampling SVM T s T 1 T 2 Carrier T 1 I 1 I 2 I 0 I 1 I 2 I 0 I 1 I 2 I 0 π/6 π/18 π/18 π/6 π/6 T 1 T 2 T 1 T s Conventional SVM [5] Carrier I 1 I 2 I 0 I 1 I 2 I 0 I 1 I 2 I 0 π/18 π/18 π/6 T s T 1 T 2 θ 2 θ 1 Multisampling SVM [6] T 1 θ 3 θ 6 θ 4 Carrier wt wt I w5 /I w1,max % I w7 /I w1,max % 8 Conventional SVM 7 f sp =1080 Hz 6 Conventional SVM f sp =1080 Hz Multisampling SVM Multisampling SVM f 4 3 sp =4*1080 Hz f sp =4*1080 Hz NSSVM f sp =1080 Hz NSSVM f sp =1080 Hz m a m a Natural sampling SVM Superior loworder harmonics performance High dynamic performance Low switching frequency θ 5 π/6 I 1 I 2 I 0 I 1 I 2 I 0 I 1 I 2 I 0 π/18 π/18 π/6 Natural sampling SVM [78] wt 10

11 Control for CSCBased Configuration v wn Overall Control Strategy Offshore Wind Farm Modular Converters 690/4000 V #n HVDC L dc1 Onshore Connection MV CSC #m v w2n #2n L dc2 #2m Multiwinding transformers Optimal generator control Voltage balancing control (4kV unit) Current balancing control (690V unit) DClink overvoltage elimination DClink inductance minimization Optimal DClink current control Control under bipolar operation Power balancing control of CSCs Optimization of onshore converters Coordinated control of the wind farm Independent offshore converters control Centralized onshore converters control Coordinated wind farm control 11

12 Control for CSCBased Configuration Independent Offshore Converters Control 4000 V MV PMSG MV PMSG v C1 v C2 S 11 S 12 S 13 S 14 d 1 i p d 2 v C3 d 3 V dc_n L dc L dc 1200 S 1 S 3 S 5 i w i g Transformer V C1 w m P g v C4 v C5 d 4 d 5 (V) S 4 S 6 S 2 C f V C2 V C3 Capacitor Voltage d 1 Sharing Scheme d 1 v C1 d 2 v C1 v C2 v C3 v C4 v C5 1 5 V c_ref v C2 v C5 d 1 d 2 d 3 d 4 d 5 d 2 d 5 d 5 d com From MPPT t (s) With Voltage Balance Control V C5 Without Voltage Balance Control V C4 With Voltage Balance Control Mediumvoltage turbine configuration [3] Optimal generator control ensured Capacitor voltage balancing ensured 12

13 Control for CSCBased Configuration Independent Offshore Converters Control 690 V LV PMSG S 11 S 12 i p S 13 S 14 V dc_n L dc S 1 S 3 S 5 i w i g Transformer S 4 S 6 S C f `I m4 `I m5`i m6 Average Current d 1 Sharing Scheme d 1 i m1 i m2 i m6 `X I m1 I m2 I m6 I m_ref 1 6 d 1 d 6 d 2 I m1 I m2 I m6 d 2 d 6 d 2 d 6 d com From MPPT (A) `I m1`i m2`i m3 Without Current Balance Control t (s) Lowvoltage turbine configuration [4] Optimal generator control ensured Average current balancing ensured 13

14 Control for CSCBased Configuration Offshore Wind Farm L dc Centralized Onshore CSCs Control V dc V dc1 Onshore PWM CSCs S 11 S 13 S 15 a b S 14 S 16 S 12 c PWM CSC #1 i w1 o L g1 C f1 Dclink Current (A) m a α V dcm_ref UPF V dcm_ref UPF P dc ma m a1 α V dc1 α 1 θ 1 1 m ma m am α V dcm P dc V dc α m V dcm_ref m a1 α 1 m am α m CSI_#1 CSI_#m S m1 S m3 S m5 i wm L gm 4500 θ m Proposed combined scheme s V dcm S m4 S m6 S m2 PWM CSC #m C fm 14 Average Input Voltage (V) Conventional DClink current control ensured Reactive power control ensured Power balancing ensured [9] V d2 V d1 Conventional & Power factor control Propsoed s 1 2

15 Control for CSCBased Configuration Monopolar vs Bipolar Operation #1 L dc #1 _ref Monopolar R l #n #m Multiwinding transformers Bipolar #1 L dc 1 #1 _ref1 R l _ 1 o I o #n 2 #m Multiwinding transformers _ref2 R l_2 Bipolar Operation Lower insulation level Higher efficiency [10] 15

16 Conclusions Configuration: MFTbased CSC seriesconnected configuration: small size and weight Modulation: Natural sampling SVM: superior loworder harmonics performance, high dynamic performance, and low switching frequency Control scheme: Independent offshore converter control, centralized onshore converters control, and coordinated wind farm control: simple, reliable and efficient 16

17 References [1] [2] M. Popat, B. Wu, F. Liu and N. Zargari, Coordinated control of cascaded current source converter based offshore wind farms, IEEE Trans. on Sustainable Energy, vol. 3, no. 3, pp , [3] Q. Wei, B. Wu, D. Xu and N. R. Zargari, "A MediumFrequency TransformerBased Wind Energy Conversion System Used for CurrentSource ConverterBased Offshore Wind Farm," IEEE Trans. on Power Electronics, vol. 32, no. 1, pp , Jan [4] Q. Wei, B. Wu, D. Xu, N. R. Zargari, "A New Configuration Using Current Source Converters in Low Voltage TurbineBased Wind Energy Conversion Systems," IEEE Journal of Emer and Selec Topics in Power Electro., vol. 6, no. 2, pp , June [5] B. Wu, HighPower Converters and AC Drives. New York/Piscataway, NJ: Wiley/IEEE Press, [6] J. Dai, Y. Lang, B. Wu, D. Xu, and N. R. Zargari, "A Multisampling SVM Scheme for Current Source Converters With Superior Harmonic Performance," IEEE Trans. On Power Electr., vol. 24, pp , [7] Q. Wei, B. Wu, D. Xu and N. R. Zargari, "A NaturalSamplingBased SVM Scheme for Current Source Converter with Superior LowOrder Harmonics Performance," IEEE Transactions on Power Electronics, vol. 31, no. 9, pp , Sept [8] Q. Wei, B. Wu, D. Xu and N. R. Zargari, "Optimal Space Vector Sequence Investigation Based on Natural Sampling SVM for MediumVoltage CurrentSource Converter," IEEE Transactions on Power Electronics, vol. 32, no. 1, pp , Jan [9] Q. Wei, B. Wu, D. Xu, N. R. Zargari, "Power Balancing Investigation of Side SeriesConnected Current Source Inverters in Wind Energy Conversion Systems," IEEE Transactions on Industrial Electronics, vol. 64, no. 12, pp , Dec [10] Q. Wei, B. Wu, D. Xu and N. R. Zargari, "Bipolar Operation Investigation of PWM Current Source ConverterBased Wind Energy Conversion Systems," IEEE Transactions on Power Electronics, vol. 33, no. 2, pp , Feb

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